The present disclosure relates to a fixing device fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
An electrographic image forming apparatus, such as a copying machine or a printer, includes a fixing device fixing a toner image on a recording medium, such as a sheet. In the fixing device, a “heat roller manner” is widely applied in viewpoints of heat efficiency, safety and others. The heat roller manner is a manner using a pair of rollers to form a fixing nip. On the other hand, a “belt manner” recently attracts attention due to requests of shortening of a warm-up time, energy saving or others. The belt manner is a manner using a fixing belt to form the fixing nip.
For example, there is a fixing device including a fixing belt, a pressure rotating body coming into pressure contact with the fixing belt, a nip member pressing the fixing belt toward a side of the pressure rotating body, a supporting member supporting the nip member and a heating source emitting radiant heat.
In the fixing device with such a configuration, there is a problem that, if the fixing belt is directly heated by the heating source, the temperature of the fixing belt is excessively risen and quality (heat resistance) of grease used between the fixing belt and nip member is deteriorated. In addition, there is a problem that the fixing belt is deformed due to the excessive temperature rise of the fixing belt, and accordingly, contact between a contact type temperature detecting part (a thermistor) and the fixing belt is lost and normal control becomes impossible or a distance between a non-contact type excessive temperature rise preventing device (a thermostat) and the fixing belt is varied to cause unsuitable operation of the excessive temperature rise preventing device.
By contrast, there is a configuration that a heat conducting member coming into contact with an inner circumference face of the fixing belt is heated by the heating source and the fixing belt is heated by heat conduction from the heat conducting member. In this configuration, the radiant heat emitted from the heating source is reflected by a reflecting member.
However, in the above-mentioned configuration, there are possibilities that, when the fixing belt is deformed according to the rotation of the fixing belt, contact failure between the heat conducting member and fixing belt is caused, heat conduction efficiency from the heat conducting member to the fixing belt is deteriorated, and temperature rise rate of the fixing belt is lowered. In addition, there are problems that, if the heat conduction efficiency from the heat conducting member to the fixing belt is deteriorated as mentioned above, a temperature difference between the fixing belt and heat conducting member is increased and the excessive temperature rise (overshoot) of the fixing belt occurs when the rotation of the fixing belt is stopped.
Moreover, in the above-mentioned configuration, there are possibilities that a part of the radiant heat from the heating source is absorbed by the reflecting member, and then, the temperature of the reflecting member is rapidly risen. If the temperature of the reflecting member is thus rapidly risen, there are problems that the temperature of a member supporting the reflecting member is excessively risen to cause deformation of the member and the excessive temperature rise (the overshoot) of the fixing belt occurs by the heat conduction from the reflecting member when the rotation of the fixing belt is stopped.